The present invention relates to a nut tensioning device, i.e., a device that applies and retains tension to a stud or bolt.
Studs and/or bolts are tensioned in order to provide a secure mechanical connection between structural members, such as, for example, a pair of opposing flanges on a piece of machinery. Tensioning of a stud or bolt is typically accomplished by a tensioning system or device that applies an axially-directed force to the stud in a direction away from the structural member. The tensioning device generally includes a gripping means and a load cell. An axially-directed force is applied by the load cell to the gripping means. The gripping means transfers the force to the stud, and thereby axially tensions or stretches the stud. The stud is then mechanically retained in its stretched or tensioned position by, for example, a nut that threadingly engages external threads formed on the stud and which is tightened down to engage the flange.
Some conventional tensioning systems utilize mechanical load cells, whereas other tensioning systems use hydraulic load cells. Mechanical load cells convert mechanical pressure or force to the axial tensioning force, whereas hydraulic load cells convert hydraulic pressure to the axial tensioning force. Tensioning systems may be configured as either internal, external or integrated tensioning systems.
External tensioning systems have a gripping means that engages threads formed on the exterior of the stud. Thus, the stud must extend a sufficient amount beyond the nut to enable adequate engagement of the gripping means on the threaded exterior of the stud. Further, the load cell of an external tensioning system is disposed over the end of and surrounds the stud and nut. Thus, there must be a certain degree of separation between the stud and nut being tensioned and any adjacent stud/nut disposed on the same structural member or flange. In other words, an external tensioning system has a large xe2x80x9cfoot printxe2x80x9d which may render it unsuitable for use in applications wherein multiple studs are in relatively close proximity with each other.
Internal tensioning systems utilize a gripping means that engages an internally threaded feature, such as, for example, a bore, defined by or formed in the stud. Thus, the stud must include the specially-formed internally threaded feature to receive the gripping means. Further, and similar to the external tensioning system, internal systems require a relatively large footprint.
Integrated tensioning systems integrate the load cell with the nut. The nut forms a nut piston and a nut cylinder. The nut piston is threaded onto external threads formed on the stud, and the nut cylinder engages the flange. The load cell, such as, for example, a hydraulic chamber, is formed between the nut piston and nut cylinder. The load cell is actuated to displace the nut piston axially away from the nut cylinder and away from the structural member or flange, thereby stretching the stud. Unlike the internal and external tensioners, the integrated tensioner must remain in place in order to maintain tension on the stud since the nut is an integral part of the tensioner. Further, in order to maintain the stud in its tensioned/stretched state, the load cell must remain actuated or pressurized. Thus, in the case of an integrated tensioner having a hydraulic load cell, the hydraulic fluid must remain in the chamber when the part or flange to which the tensioner is affixed is placed into service. The hydraulic fluid, depending on the particular application, may degrade, such as, for example, due to exposure to high operating temperatures. Furthermore, the hydraulic fluid may over time leak or solidify, making removal of the tensioner problematic. Moreover, the hydraulic chamber defined by the integrated system has a relatively limited capacity and therefore the integrated system has a correspondingly limited load capacity. Similar disadvantages exist for mechanical load cells.
Therefore, what is needed in the art is a tensioner device that does not require a specially configured stud or a stud that extends beyond the nut.
Furthermore, what is needed in the art is a tensioner device having a relatively small footprint.
Still further, what is needed in the art is a tensioner device with a relatively large load capacity.
Even further, what is needed in the art is a tensioner device that is suited for retrofit applications, such as, for example, when the surface of the structural member surrounding the nut is not suitable for being engaged by a conventional tensioning system, or when there is no suitable surface on the stud to which a conventional gripping means can be attached.
The present invention provides a stud or bolt tensioning system for tensioning a stud or bolt extending from a structural member.
The invention comprises, in one form thereof, a nut having internal threads and external threads. The internal threads engage corresponding threads on the stud. At least two axial bores are defined by the nut, and posts are disposed in the bores. Each post at a first end thereof engages a stop surface, and at a second end thereof extends external to the bores and axially beyond a free end of the stud in a direction away from the structural member. A load cell threadingly engages the nut applying an axially-directed force on the posts in a direction toward the structural member and on the nut in a direction away from the structural member to thereby tension the stud.
An advantage of the present invention is that it has a relatively small footprint, and can therefore be used for tensioning finely-pitched studs or closely-spaced studs.
Another advantage of the present invention is that it has a relatively large load capacity.
Yet another advantage of the present invention is that it is well-suited for retrofit applications, such as, for example, where there is no suitable surface surrounding the nut against which a conventional tensioning system could act and/or no suitable surface on the stud to which a conventional gripping means can be attached.
A still further advantage of the present invention is that the load cell grips the nut, and thus the present invention does not require a footprint outside the nut. Thus, no special features are required on the stud for engaging the tensioner.